Fuel oils having improved burning characteristics



United States Patent Ofiice 3,066,018 Patented Nov. 27, 1962 3,056,018FUEL OILS HAVING EMPRQVED EURNINQ CHARACTERKSTEQ "Robert J. McGuire,Monroevilie, Pa, assignor to Gulf Research & Deveiopment @ornpany,Fittshurgh, Pa, a corporation of Delaware No Drawing. Filed June 6,196%, 5131. No. 33,933 it Claims. (Cl. 44-66) heavier fuel oils that canbe burned in fuel burners, such as those of the atomizing type and ofthe rotary wall flame type, with little or no accompanying formation ofsmoke or soot. Oils that are normally burned in oil burners of the typesindicated are those of No. 2 grade or heavier, although somewhat lighteroils can be used.

.Although some smoke and soot formation may accompany combustion of anyhydrocarbon oil where less than optimum combustion conditions are used,the problem is serious in the case of oils having an API gravity of lessthan 34, as substantial smoking and soot formation will occur duringcombustion of such oils even when favorable combustion conditions areemployed. The poor combustion characteristics of such oils areconsidered attributable to the relatively high proportion of aromaticcomponents contained therein. Fuel oils having an API gravity of lessthan 34 will normally contain in excess of about 20 percent aromatics,for example, 25, 40, or even-6t) percent or more of aromatic components,whereas lighter fuel oils will normally contain a substantially lowerproportion of -aromatics, for example, 15 percent orless. In the case ofdistillate oils, a high aromatics content usually signifies a largeproportion of cracked distillates, as the latter are relatively rich inaromatics. The proportion of catalytically cracked distillate fuel oilsin commercially marketed fuel oils has increased in recent yearsnotwithstanding the relatively inferior burning qualities of such oils,because the demand for fuel oils or comparable boiling range hasexceeded the available supply of straight-run oils.

Not only do low-gravity distillate oils containing large proportions ofcracked. distillate, that is, oils rich in aromatics, form greaterquantities of soot during combustion than straight-run, high-gravitydistillate oils, or similar oils low in aromatics,but also such oilsform soot of different quality. Soot formed from the latter oils is aloosely deposited, low-density material having a low coefficient of heattransfer, whereas soot from the former oils is resinous, much denser andhas a higher coetficient of heat transfer.

While the problem of obtaining clean combustion is especially'serious inthe case of distillate fuels, where fuel quality is of major importance,a combustion problem also exists in the case of residual fuel oils.Residual fuels, similarly as middle distillate fuel oils, have an APIgravity less than 34 (API gravity for typical No. 6 fuel oils varies inthe range of about to 15), and they also frequently containexceptionally large proportions, for example 60 percent or more, ofaromatic components. Residual fuels can contain relatively low-boilingaromatic components as well as higher boiling materials, as they arefrequently diluted or cut back with lower boiling cracked distillateoils in order to reduce the viscosity of the heavier oils.

Although the combustion of fuel oils having an API gravity of less than34, and consequently a' relatively large proportion of aromatics, willtend to produce soot and smoke in atomizing type burners, that is,burners in which the fuel oil is burned in the form of a spray of liquiddroplets after mixture with air, combustion of such oils in rotarywall-flame type burners constitutes an especially severe problem. In thelatter instance the fuel oil is burned in vapor form after vaporizationof the fuel by impingement thereof on a hot metal surface.

The present invention relates to the improvement'of hydrocarbon fuel oilcompositions that normally tend to form smoke and soot duringcombustion, whereby such oils are rendered more suitable for use asfuels in domestic oil burners of various types such as heating furnacesof the atomizing or rotary, wall-flame type, combustion gas turbineengines, and the like. It has now been found that such improved fuelcompositions can be obtained by incorporating in a fuel oil of the typedescribed a small amount of a triester of a hexitan and a fatty acidcontaining 12 to 20 carbon atoms per molecule,- or a polyoxyethylenederivative of a partial ester of a hexitan and a fatty acid containing12 to 20 carbon atoms per molecule. sorbitan is the preferred hexitanfor purposes of the present invention as are faty acids containing 18carbon atoms per molecule. It is preferred to employ polyoxyethylenederivatives that contain a total of about 3 to 9 ethoxy groups permolecule, but other polyoxyethylene derivatives can be used. Thus, therecan be used polyoxyethylene derivatives that contain a total of about 3to 30 ethoxy groups per molecule. Specific examples of preferredmaterials included by this invention are sorbitan trioleate and apolyoxyethylene derivative of sorbitan nonooleate containing a total ofsix ethoxy groups per molecule. However, other materials disclosedherein can be used. Examples of such other materials are mannitantrioleate, dulcitan trioleate, and polyoxyethylene derivatives ofsorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate, andsorbitan monolaurate containing 3, 6, or 21 ethoxy groups per molecule,and polyoxyethylene derivatives of sorbitan trioleate and sorbitantristearate containing 2 or 6 ethoxy groups per molecule. The hexitanesters and polyoxyethylene derivatives thereof disclosed herein arepreferably employed in the fuel oil compositions of this inveintion isproportions in the range of 0.01 percent to 0.1 percent by weight of thecomposition, but other proprtions can be used.

The exact mechanism by which the hexitan esters and polyoxyethylenederivatives thereof of the herein-disclosed class function to reducesmoke and soot forming tendencies of fuel oils has not been definitelydetermined, and accordingly, it is not intended that the presentinvention be limited to any particular theory of operation. It has beenhypothesized that the hexitan esters and polyoxyethylene derivativesthereof Whose use is included by this invention possess a criticalbalance of surface-active properties such as to promote a reduction inthe size of the fuel droplets sprayed into the combustion zone of theburner and/0r such as to promote an improvement in the spray pattern.This view is more or less supported by the fact that compounds bearing aclose chemical similarity to the materials disclosed herein have beenfound to be substantially less efiective in reducing the smoke and sootforming tendencies of fuel oils. However, the above-indicated hypothesiswould appear to'be somewhat negatived by the fact that the combustioncharacteristics of fuel oils in rotary, wall-flame burners that do notinvolve spraying the fuel are also improved by the herein-disclosedmaterials.

As disclosed above, the materials found effective for the purposes ofthis invention include triesters of hexitans and higher fatty acids thatcontain 12 to 20 carbon atoms 3. per molecule, and polyoxyethylenederivatives of partial esters of hexitans and fatty acids containing 12to 20 carbon atoms per molecule. Best results are obtained when thetriesters or polyoxyethylene derivatives disclosed herein are liquidshaving a viscosity not greater than 600 centipoises at 25 C.

The esters referred to herein are, as indicated, derived from higherfatty acids containing 12 to 20 carbon atoms per molecule,representative members of which are lauric, palmitic, oleic, and stearicacids. Esters derived from oleic acid are preferred for the purposes ofthis invention by reason of their low viscosity and fluidity, wherebyformation of homogeneous mixtures with fuel oil is facilitated.

The polyoxyethylene derivatives of the hexitan fatty acid partial esterswhose use is included by the present invention can be represented by thegeneral formulas:

and No. 6 fuel oils, and the use of such oils is included by the presentinvention. Fuel oils of these grades are defined in the ASTM Standardson Petroleum Products and Lubricants under the ASTM Specification D396.The invention is especially important in connection with fuel oilshaving an API gravity of less than 34, particularly when these oilscontain an excess of about percent aromatic hydrocarbons, as such oilsinvolve serious smoke and soot forming problems.

In order to demonstrate the effectiveness of the materials of the classdisclosed herein, representative members of such class were incorporatedin samples of No. 2 fuel oil and the thus-compounded fuel oils weresubjected to a full scale, one day smoke test in a domestic oil burner(Timken Model OBC-llO, Oil-boiler). Conventional burner controls wereassociated with the test apparatus in conjunction with electrical timerrelays to provide I I RCO 0 CHQOHCHO (CHzCHzO) XHCHO (CH2CH20)yHCHO(CHzCHzO) lHGH:

where R is the hydrocarbon radical component of a higher fatty acid, andx, y, and z are like or unlike numbers of 1 to 10, preferably, 1 to 3.An example of a preferred polyoxyethylene hexitan partial ester is oneof the formula indicated above where R is a 17 carbon atom alkenylsubstituent and x, y, and z are each 2.

The hexitan esters and derivatives employed in this invention need notbe pure and commercial materials can be used. Examples of such materialsare sorbitan trioleate, the polyoxyethylene sorbitan monostearate, andthe polyoxyethylene sorbitan monooleate marketed, respectively, as Span85, Tween 60, and Tween 81.

The hexitan esters and polyoxyethylene derivatives thereof disclosedherein can be employed in fuel oils in any proportion that will reducethe smoke and soot forming tendencies of the oils. The optimumproportion in any given case can vary in accordance with the individualaddition agent and in accordance with the nature of the fuel oil, as allof the materials disclosed herein are not exactly equivalent in theirability to improve the combustion characteristics of fuel oils, and asall fuel oils are not equally responsive to such materials. Normally,some improvement in the combustion characteristics of fuel oils of thekind disclosed herein can be obtained by the use of as little as 0.01percent of the materials disclosed herein. A major improvement isnormally obtainable by the use of proportions in the range of about 0.03to 0.07 percent by weight of the fuel oil. Normally no additionaladvantage with respect to smoke and soot formation during combustion isobtained by the use of amounts in excess of about 0.1 percent by weightof the fuel oil. In fact, it has been found that amounts in excess ofabout 0.1 percent, although still effective to reduce smoke and sootformation, actually can be less beneficial from the standpoint of smokeand soot reduction than amounts of 0.1 percent or less.

The hexitan esters and polyoxyethylene derivatives thereof disclosedherein can be added to fuel oils whose combustion characteristics are tobe improved either as such or in the form of concentrated solutions insolvents such as kerosene or toluene. If desired, the esters andderivatives disclosed herein can also have included therewith otheraddition agents designed to improve one or more properties of the fueloil. Some agitation will normally be desirable when mixing theherein-disclosed materials with fuel oil in order to facilitate rapidformation of a homogeneous mixture, but agitation is not essential.

As indicated, the hexitan esters and polyoxyethylene derivatives thereofdisclosed herein are useful in conjunction with any fuel oil thatnormally tends to form 20-minute on and IO-minute off cycles of burneroperation. After permitting a warm-up of at least one 20-minute on cycleof burner operation with maximum combustion air, smoke spot number andcarbon dioxide content readings were taken on the flue gas at the middleof the on phases for several cycles using different air gate settings toregulate the quantity of combustion air. Changes of gate setting weremade during burner oiF phases of the cycle. Smoke spot readings wereobtained by withdrawing flue gas from a sampling probe installed in thechimney pipe through a disc of a No. 4 Whatman filter paper one inch indiameter for two minutes. A vacuum pump was used to maintain a pressuredifferential of 2% inches Hg across the disc. The smoke spot rating wasdetermined by means of a photo-cell meter that had been calibrated by aBacharach-Shell smoke spot chart graduated in increasing shades of blackranging from 0 (clean disc) to 9 (black disc) as the standard. COreadings were obtained by withdrawing flue gas through a sampling probeinstalled in the chimney pipe in accordance with the United StatesDepartment of Commerce Bulletin CA104-46, and by analyzing thethus-withdrawn flue gas for percent CO in an Orsat-type flue gasanalyzer.

Two different fuel oils were employed in the abovedescribed tests. Thefirst oil, hereinafter referred to as Base Fuel A, was a blend of 35percent by volume West Texas straight-run and 65 percent by volume fluidcatalytically cracked No. 2 fuel oil distillate having an API gravity of29.3 and an aromatics content of 45.0 percent by weight. The other fueloil employed in the test, hereinafter referred to as Base Fuel B, was ablend of 17.5 percent by volume of a mildly hydrogenated West Texasstraight-run and 82.5 percent by volume of a fluid catalytically crackedNo. 2 fuel oil distillate having an API gravity of 29.6 and an aromaticscontent of 42 percent by weight.

The materials employed in the tests included Span 85, Tween 60, andTween 81. Span is a commerical sorbitan trioleate that is normally inthe form of an amber, thin, oily liquid having a viscosity in the rangeof about to 250 centipoises at 25 C., a specific gravity of about0.92-0.98, a flash point of about 500 F. and a fire point of about 570F. Tween 60 is a commercial polyoxyethylene sorbitan monostearate thatis normally in the form of a lemon-orange, oily liquid having aviscosity in the range of 400 to 600 centipoises at 25 C., specificgravity of about 1.05-1.10, a flash point of about 545 F., and a firepoint of about 635 F. Tween 81 is a commercial polyoxyethylene sorbitanmonooleate that is normally in the form of a lemon-colored, oily liquidhaving a viscosity in the range of about 350 to 550 centipoises at 25C., a specific gravity of about 1.00-1.05,

5 a flash point of about 550 F. and a fire point of about 600 F. Thematerial employed in the tests had an absolute viscosity of 456.8centipoises at 77 F. and an average molecular weight of 722. The lattervalue corresponds to an average of about 6.6 ethoxy groups per molecule.

The smoke spot numbers obtained in the above-described tests when the COcontent of the flue gas was 12 percent, that is, the level at whichminimum smoke and soot was produced by the uninhibited fuel oil, arepresented below.

Table A Additive Propor- Smoke Make-Up tion, Spot N Percent 12% CO2 byWt.

Base Fuel A- 1. 25 +Sorbitan Trioleate 0.06 1. 0 +PolyoxyethyleneSorbitan Monostearate. 0. 06 0. 95

Base fuel B 2. 2 +Polyoxyethylene Sorbitan Monooleate 0.05 1. 95+Polyoxyethylene Sorbitan Monooleate- 0.5 2.0

The results set forth in the preceding table clearly demonstrate theeffectiveness of the hexitan esters and polyoxyethylene derivativesthereof of the class disclosed herein to reduce smoke and soot formationin actual operation in domestic fuel oil burners. The results set forthin the preceding table also demonstrate the especial effectiveness ofproportions in the range of 0.01 to 0.1 percent by weight of the fueloil composition.

'It will be understood that the specific embodiments set forthhereinabove are illustrative only and that the invention is not limitedto the use of the specific materials or proportions disclosed therein,and that good results can be obtained by the substitution in theforegoing embodiments of other fuel oils disclosed herein and by thesubstitution in the same or equivalent amounts of other hexitantriesters or other polyoxyethylene derivatives of hexitan fatty acidpartial esters disclosed herein.

Examples of other compounded fuel oils containing materials of the typewhose use is included by the present invention are indicated in thefollowing table:

Table B Addition Agent; Concentration, Percent by Wt.

Base Fuel 0.06 Base Fuel A.

Polyoxyethylene Sorbitan Dllaurate 0. 06 Base Fuel B PolyoxyethyleneSorbitan Trloleate Gravity.

The term hexitans is employed herein in its conventional sense toindicate the intramolecular anhydrides derived from hexitols such assorbitol, mannitol and dulcitol. These anhydrides are normallyconsidered to comprise a mixture of inner anhydrides containing 5- and6-membered, oxygen-containing, heterocyclic rings.

If desired, the fuel oil compositions of this invention may contain inaddition to the compounds previously disclosed herein oxidationinhibitors, corrosion inhibitors, antifoam agents, sludge inhibitors,color stabilizers, and/or other addition agents adapted to improve theoils in one or more respects.

Obviously, other modifications and variations of the invention asherein-described may be resorted to without departing from the spirit orscope hereof. Therefore, only such limitations should be imposed as areindicated in the appended claims.

I claim:

1. A fuel oil composition comprising a major amount of a hydrocarbonfuel oil that normally tends to form smoke and soot during combustion,and a small amount, sufficient to reduce the smoke and soot formingtendencies of the oil, of a member selected from the group consisting ofa triester of a hexitan and a fatty acid containing 12 to 20 carbonatoms per molecule and a polyoxyethylene derivative of a partial esterof a hexitan and a fatty acid containing 12 to 20 carbon atoms permolecule, where said polyoxyethylene derivative contains 3 to 30 ethoxygroups per molecule, said small amount being in the range of about 0.01to 0.1 percent by weight.

2. The fuel oil composition of claim 1 where said hydrocarbon fuel oilis a distillate fuel oil 3. The fuel oil composition of claim 1 wheresaid hydrocarbon fuel oil has an API gravity less than about 34.

4. The fuel oil composition of claim 1 where said small amount is in therange of about 0.03 to 0.1 percent by weight.

5. The fuel oil composition of claim 1 where said member is an oilyliquid having a viscosity not greater than about 600 centipoises at 25C.

6. A fuel oil composition comprising a major amount of a hydrocarbonfuel oil that normally tends to form smoke and soot during combustion,and a small amount, sufiicient to reduce the smoke and soot formingtendencies of the oil, of a triester of a fatty acid containing 12 to 20carbon atoms per molecule, said small amount being in the range of about0.01 to 0.1 percent by weight.

7. A fuel oil composition comprising a major amount of a hydrocarbonfuel oil that normally tends to form smoke and soot during combustion,and a small amount, suificient to reduce the smoke and soot formingtendencies of the oil, of sorbitan trioleate, said small amount being inthe range of about 0.01 to 0.1 percent by weight.

8. A fuel oil composition comprising a major amount of a hydrocarbonfuel oil that normally tends to form smoke and soot during combustion,and a small amount, sufficient to reduce the smoke and soot formingtendencies of the oil, of a polyoxyethylene derivative of a partialester of a hexitan and a fatty acid that contains 12 to 20 carbon atomsper molecule, where said polyoxyethylene derivative contains 3 to 30ethoxy groups per molecule, said small amount being in the range ofabout 0.01 to 0.1 percent by weight.

9. A fuel oil composition comprising a major amount of a hydrocarbonfuel oil that normally tends to form smoke and soot during combustion,and a small amount, sufiicient to reduce the smoke and soot formingtendencies of the oil, of a polyoxyethylene derivative of a partialester of a heXitan and a fatty acid that contains 12 to 20 carbon atomsper molecule, where said polyoxyethylene derivative contains 3 to 9ethoxy groups per molecule, said small amount being in the range ofabout 0.01 to 0.1 percent by weight.

10. A fuel oil composition comprising a major amount of a hydrocarbonfuel oil that normally tends to form smoke and soot during combustion,and a small amount, sufficient to reduce the smoke and soot formingtendencies of the oil, of a polyoxyethylene derivative of sorbitanmonooleate containing about six ethoxy groups per molecule, said smallamount being in the range of about 0.01 to 0.1 percent by weight.

References Cited in the file of this patent UNITED STATES PATENTS Caronet a1 Apr. 10, 1951 Rogers Feb. 12, 1952 OTHER REFERENCES

1. A FUEL OIL COMPOSITION COMPRISING A MAJOR AMOUNT OF A HYDROCARBONFUEL OIL THAT NORMALLY TENDS TO FORM SMOKE AND SOOT DURING COMBUSTION,AND A SMALL AMOUNT, SUFFICIENT TO REDUCE THE SMOKE AND SOOT FORMINGTENDENCIES OF THE OIL, OF A MEMBER SELECTED FROM THE GROUP CONSISTING OFA TRIESTER OF A HEXITAN AND A FATTY ACID CONTAINING 12 TO 20 CARBONATOMS PER MOLECULE AND A POLYOXYETHYLENE DERIVATIVE OF A PARTIAL ESTEROF A HEXITAN AND A FATTY ACID CONTAINING 12 TO 20 CARBON ATOMSPERMOLECULE, WHERE SAID POLYOXYETHYLENE DERIVATIVE CONTAIN 3 TO 30ETHOXY GROUPS PER MOLECULE, SAID SMALL AMOUNT BEING IN THE RANGE OFABOUT 0.01 TO 0.1 PERCENT BY WEIGHT.